Networks

• connectivity and structure of neural activity theoy side - https://www.sciencedirect.com/science/article/pii/S1364661324000561?dgcid=author

• Impact of Infralimbic inputs on Amygdala neurons. Biophysical modelling - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3072774/

• https://www.jneurosci.org/content/jneuro/42/15/3165.full.pdf - Seperate sub networks for periodic deviant and random deviant

• Homophilic wiring principles underpin neuronal network topology in vitro (biorxiv.org) - modelling of wiring of neurons of similar type - modelling

• https://www.biorxiv.org/content/10.1101/512053v1.full -Systematic errors in connectivity inferred from activity in strongly coupled recurrent circuits

• Cortical glutamatergic projection neuron types contribute to distinct functional subnetworks from Josh Huang’s lab https://www.nature.com/articles/s41593-022-01244-w

• Neural networks analysis theory thesis https://uwspace.uwaterloo.ca/bitstream/handle/10012/12173/caterini_anthony.pdf

• Spontaneous symmetry breaking concept in Visual cortex Mechanisms for Spontaneous Symmetry Breaking in Developing Visual Cortex (aps.org)

• The logic of recurrent circuits in the primary visual cortex | bioRxiv - 2p, opto, recurrent network in v1

• How top down and bottom up inputs are integrated - computer simulations constrained by experimental observations - Sparse bursts optimize information transmission in a multiplexed neural code | PNAS

• On the computational architecture of the neocortex

Part 1 - The role of the thalamo-cortical loop

Cortex has 6 layers

Thalamus is below cortex, its like the 7th layer

except RE nucleus in Thalamus, all nuclei give output and take input from cortex. The neurons n

Thus, except for the RE nucleus, the nuclei in the thalamus are not directly connected to each other

but, by and large, their largest input[to thalamus] is from the cortex itself, via the reciprocal cortico-thalamic pathways described above

The simplest hypothesis is that the specific projections set up reciprocal maps between the whole of the cortex and the specific nuclei of the thalamus which are roughly one-to-one in each direction. 7 Alternately, each nucleus in the thalamus may communicate to one or more cortical areas via specific projections

If the thalamus is the gateway to the cortex, the reticular complex might be described as the guardian of the gateway. Its exact function is unknown

Imp question - single-cell recordings all suggest that the thalamus does little or no computation by itself. But if it is merely a relay station, a) why do even association areas of the cortex receive thalamic input and b) why does the cortex reciprocate with a massive projection of fibres back to the thalamus? Both of these are biologically very expensive

A: in the ‘higher’ sensory areas this would mean that the thalamus sends them not the raw sensory data but a processed version of the input in which noise and irrelevant stuff have been dropped, and the interesting features are marked as such.

Why thalamus in middle?

A: thalamus sends them not the raw sensory data but a processed version of the input

why reciprocal connections to thalamus from cortex?

A:

Blackboard theory of Mumford

• Thalamic → Cortex: Each region of cortex receives processed/filtered from certain region of thalamus.
• Cortex → Thalamus: Cortex can be thought of as collection of independent experts - experts in pattern recognition, constraints understanding. These independent experts(cortical regions) project onto thalamus to use thalamus as an active blackboard. Cortical regions output/decision is projected onto thalamus to integrate multiple decisions/choose the best based on voting.

(Note that the biggest input to thalamus is from the Cortex)

Explanation for Diffuse and Specific projections:

1. Specific Projections - One particular region of thalamus gives to only one particular region of cortex
2. Diffuse Projections - One particular regions give to different regions of cortex and takes input from different regions of cortex

Diffuse Projections on thalamus(from different regions of cortex) can be used for combining results of different experts(different regions).

For example MT in cortex calculate movement

V2 and V4 work on figure and ground.

These regions project on pulvinar complex of thalamus, whether figure and ground may be used to combine with movement for more information. Note that this same could be achieved by interaction between MT, V2 and V4 without involving thalamus. So, there are 2 ways for combining results of different cortical regions - Cortico-cortical connections and Cortico-thalamic connections.

cortex contains multiple independent ‘experts’ which analyze different aspects of each area’s data and that their results are merely integrated in the thalamus

hierarchic structure with extensive reciprocal connections.

Motor pathway

Apart from Motor Cortex and thalamus interaction, cerebellum is also involved. cerebellum function: modifies and specifies in detail what combination of forces for what periods of time in which muscle groups best carry out this command.

Cerebellum → VPthalamus → Motor cortex/Premotor → Spinal Cord

(Pyramidal tract- path from cerebellum to brain stem/spinal cord)

(a polished movement is executed with help of cerebellum)

Shocking fact➖

Thus the cortical input to the LGN is about 40 times bigger than the retinal input, and 13 times bigger than the reciprocal LGN to cortex pathway.

Cortical → Thalamus > Retina → Cortex

Cortical → Thalamus > Thalamus → Cortex

Thalamus for better memory and performance➖

if the thalamus is a blackboard, stimulating it could have the effect (a) of highlighting one of the data items represented on it, resulting in better memory for the item, and (b) of hindering the power of cortico-thalamic pathways to revise and update the data in the thalamus appropriately, causing persevervation and the other types of error Ojemann observes.

thalamus - integrating multiple hypotheses formed in the cortex via the thalamo-cortical loop.

Part 2 - Cortico-cortical loops

link - On the computational architecture of the neocortex (springer.com)

all most all connections are reciprocal. A projects to B, then B projects to A

interesting fact: cortex - more principal neurons(pyramidal cells(60-80). in other places like cerebellum - more interneurons than principal